Amplifier



June 1941- J. A. WORCESTER; JR 2,246,158

I AMPLIFIER Filed Aug. 17 1959 Fig.1.

AMPLIFIER Inverwtor": oseph A. Worcester, Jr.

His Attorney.

Patented June 17, 1941 2,246,158 AMPLIFIER Joseph A. Worcester, JrBridgeport, Conn., assignor to General Electric Company, a. corporationof New York Application August 17, 1939, Serial No. 290,611

' '1 Claims. (01

My invention relates to amplifiers such as are commonly used in radioreceivers and it has for one of its objects to effect certainimprovements therein with respect to means for securingdegeneration insuch amplifiers.

Commonly, the audio frequency amplifiers in radio receivers are providedwith degeneration circuits to improve the frequency responsecharacteristic, reduce hum, distortion, and for other reasons. suchamplifiers at high frequencies such circuits are likely to becomeregenerative at those frequencies. One of the objects of my invention isto provide improved means for avoiding such regeneration.

Another object of my invention is to provide means whereby, particularlyatthe higher frequencies, two voltages are supplied from the output ofthe amplifier to the input thereof having such phase relations that theresultant voltage is degenerative even though one of the two voltagesbecomes regenerative.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My invention,itself, however, both as to its organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawing in which Fig. 1 represents an embodimentof my invention; Figs. 2 and 3 represent certain vector diagramsrelating to its operation and Figs. 4 and 5 illustrate modifications.

Referring to the drawing, I have shown therein the audio frequencyportion of a conventional radio receiver, this portion comprising adetector including a diode I, which is connected in series with thesecondary Winding of a transformer 2 and a diode load resistance 3, thelatter being shunted by the usual condenser 4. This circuit is the usualdiode detector circuit of a radio receiver to which currents of radiofrequency, such as the received signal currents, or if the receiver beone of superheterodyne type, the intermediate frequency currents, aresupplied through transformer 2. These currents are rectified by thediode I to produce a direct current potential upon resistance 3 havingtherein the-audio frequency modulations of the carrier wave. These audiofrequency variations are supplied through a condenser 5 to an audiofrequency volume control potentiometer 6 from whence they are suppliedthrough a tap connection I to the input circuit of .an audio amplifier8. Currents amplified by the Due to the phase shift which occurs inamplifier 8 are additionally amplified by push-pull amplifier 9including electron discharge devices II] and I I. .The output circuit ofthese discharge devices includes an audio frequency transformer I3 thesecondary winding of which is connected across the voice coil of a loudspeaker I4.

The amplifier 9 is energized from a suitable source of potential, whichis connected between ground and the intermediate point on the primarywinding of transformer I3, this point being indicated at 3+ on thedrawing. This source, of course, may also supply the potential to thescreen grids of discharge devices Ii] and II as well as operatingpotential to the discharge devices of amplifier 8.

AS previously stated, it is now common practice in radio receivers toutilize degeneration in connection with such amplifiers in order toimprove the frequency-response characteristic, reduce distortion, and toreduce the reproduction of such hum currents as may be produced in thesystem from the power supply source where such source is derived byrectifying potentials from a commercial alternating current circuit,such as the ordinary house lighting circuit. To this end resistances I5and I6 are included, the resistance l6 being connected betweenresistance 5 and ground and the resistance I5 being connected betweenthe ungrounded terminal of resistance I6 and the ungrounded terminal ofthe voice coil of loud speaker I4. Potential is thus supplied from thevoice coil of loud speaker I4 through resistance I5 to resistance l6,which is connected between the grid and cathode of the first dischargedevice in amplifier 8, this potential being supplied to this amplifierin degenerative phase.

In such systems, however, due to certain shunt capacities employed inamplifiers 8 and 9, such as the capacities which are connected betweenthe anodes and cathodes of the various discharge devices, one of whichis indicated at I'I on the drawing, phase shift occurs at highfrequencies, this phase shift being sufficient at those frequencies tocause the potential supplied through resistance I5 to resistance I5 tobe shifted in phase sufficiently to become regenerative. This is notdesirable for a number of reasons, one being that it increases theresponse of the amplifier to extremely high frequencies therebyrendering the amplifier undesirably sensitive to noise currents.

To avoid such regeneration, in accordance with my invention, a secondvoltage is supplied from the output of the amplifier to the input of theamplifier of such phase that the resultant of the two voltages isdegenerative even at the high frequencies. In Fig. 1 this second voltageis supplied to the resistance It through condenser I8. This condenser I8may comprise the condenser normally connected between the anode ofdischarge device I I and ground after the manner of condenser II.

In accordance with my invention this condenser is connected to groundthrough resistance I6. It has such a value that its impedance is high atall frequencies to be amplified relative to the resistance of resistanceI6 so that no substantial phase shift in the voltage supplied through itoccurs by reason of change in its reactance with frequency. At lowfrequencies its reactance is so high that the voltage suppliedtherethrough is insufficient greatly to influence the phase of theresultant of the two voltages. At high frequencies, however, itsreactance, although still high relative tothe resistance of resistor I6,is sufficiently low that its voltage very materially affects the phaseof the resultant of the two voltages and it is in such a direction thatthis resultant voltage is maintained in. degenerative phase even at the.higher frequencies.

This operation of the system may be better understood from an inspectionof Figs. 2 and 3. Fig. 2 represents the condition. which exists at lowfrequencies. In this figure c represents the signal voltage supplied bythe detector I to the input of amplifier 8; e represents the voltagesupplied to. resistance It through resistance I5. this voltage being 180degrees displaced from the signal voltage e e represents the voltagesupplied through condenser I8 from the anode of device I I. Of coursethe voltage on the anodes of discharge devices It] and II are 180degrees displaced with respect to each other but this voltage is takenfrom the anode of the device from which the voltage is in lagging phasewith respect to the voltage 6g. The resultant of the two voltages e and6 is indicated at e Owing to the large impedance of condenser I8 at lowfrequencies, e is not greatly different either in phase or magnitudefrom e Fig. 3 represents the condition which exists at high frequencies.It will be seen that the voltage e supplied through resistance I5 is"now shifted to a position where it lags the signal input voltage e byless than 90 degrees. It thus has a regenerative component and tends toincrease the amplification at high frequencies. The voltage 6 is stillin the quadrature relation with respect to c but is now greatlyincreased due to the lower reactance of condenser 8 at the highfrequencies. The resultant of these two voltages 6.4", has thus notshifted in phase to the extent that e has shifted and is still indegenerative phase even at the highest frequencies to be amplified. Infact in this way any likelihood of a' regenerative condition existing athigh frequencies is eliminated.

Fig. 4- represents a modification of my invention which involves anamplifier having two stages I 9 and 20, both amplifiers being of thesingle ended type as distinct from the push-pull type shown at 9 inFig. 1. As previously pointed out in Fig. 1 the desired lagging relationof voltage e to that of a is secured by taking this voltage from theproper one of the two discharge devices IE, or II'. This selection isnot available in the arrangement of Fig. 4, which does not involve apush-pull amplifier. The same result, however, may be secured byutilizing a resistance 21 between the cathode and ground of the firstamplifier IS. The voltage e may then be supplied from the anode ofdischarge device 20 to the cathode thereof through the condenser I8which corresponds to the condenser I8 of Fig. 1. The voltage e;' issupplied through resistance I5 to resistance IS in the same way as wasdone in Fig. 1. These two voltages then combine in the input circuit inthe way that is illustrated by the vector diagrams of Figs. 2 and 3.

Fig. 5 shows a further simplification of the arrangement of Fig. 4 inthat the circuits are so arranged that resistance 2| serves the purposeof both resistances -2I and I6 of Fig. 4 thus obviating one resistor.Condenser I3 is connected as in Fig. 4. Resistance I5 is, in Fig. 5,connected between. the cathode of discharge device I9 and the oppositeside of the secondary Winding of transformer I3 from that shown in Fig.4, the ground connection to that winding being also positioned on theopposite terminal. In this way the'two voltages e and e both appear uponresistance 21 in proper phase to produce the effects above explained.

While I. have shown particular embodiments of my invention, it will, ofcourse, be understood that I do not wish to be limited thereto sincevariousmodifications both in the circuit arrangements and in theinstrumentalities employed may be made. I. therefore, contemplate by theappended claims tocover any such modifications as fall within the truespirit and scope of my invemtion- What I claim as new and desire tosecure by Letters Patent of the United States is:

1. In combination, an audio amplifier for currents having frequenciesextending over a wide range of. audiofrequenci'es, means to supplyvoltage from the outputof said amplifier to the input thereof indegenerative phase at low frequencies said range, said amplifier.pperating to shift the pham of said voltage at high fre- .quencies insaid range to a regenerative phase,

and means to combine with said voltage supplied from the output a secondvoltage supplied from the output of said amplifier of such phase thatthe resultant voltage is in degenerative phase at all frequenciesthroughout said range.

2. The method of maintaining degeneration at high frequencies in anaudio amplifier in which large phase shift occurs at such frequencies,which includes supplying from the output to the input of said amplifiertwo voltages, the resultant of which remains in degenerative phase whenone of saidvoltages is supplied in regenerative phase.

3 The method of maintaining degeneration at high. frequencies inan audioamplifier in which large phase shift occurs at such frequencies,

which includes supplying from the output to the input of said amplifiertwo voltages widely shifted irr phase, one of said voltages beingshifted in one direction from the desired phase relation at lowfrequencies and the other being shifted in the opposite direction fromthe desired phase relationat high frequencies, and the resultant ofwhich voltages remains in desired phase at all frequencies.

4. The method 01'- maintaining a desired relatlOH over a wide frequencyrange between the voltage supplied to the input of an amplifier foramplification thereby and a voltage supplied thereto from the output ofsaid amplifier, where large phase in the amplifier occurs at highfrequencies-,which includes supplying to said input from the output ofthe amplifier, two voltages whose phase shifts vary with frequency butthe resultant of which remains in the desired phase relation.

5. In combination, an amplifier, an input circuit therefor, a resistanceconnected between said input circuit and the output of said amplifier tosupply voltage from said output to the input in degenerative phase atlow frequencies, said amplifier operating to shift the phase of saidvoltage at high frequencies to a regenerative phase relation, acondenser connected between said output and input, said condenser havingsufficiently high impedance at low frequencies that only small voltageis supplied through said condenser to said input circuit and saidcondenser having sufficiently low impedance at high frequency that thevoltage supplied therethrough to said input at high frequency issufficiently great that the resultant of said voltage and that suppliedthrough said resistance is degenerative at the highest frequencies to beamplified.

6. In combination, an amplifier having an input circuit including aresistance, a resistance and a condenser each connected between theoutput of said amplifier and said first resistance to impress voltagesfrom said output on said first resistance in quadrature relation, thevoltage supplied through said resistance being in degenerative phase atlow frequencies and in regenerative phase at high frequencies, and thevoltage supplied through said condenser being low at low frequenciesrelative to that supplied through said resistance, but sufiiciently highat high frequencies that the phase of the resultant voltage on saidfirst resistance is degenerative at said high frequencies.

'7. In combination, an amplifier having a grid, a cathode and an output,said cathode being connected to ground through a resistance, an inputcircuit coupled to said grid, a condenser connected between said outputcircuit and said cath-' ode, and a second resistance connected betweensaid output and said input circuit, said second resistance operating tosupply between said grid and cathode a voltage having degenerative phaseat low frequencies and regenerative phase at high frequencies, saidcondenser having sufliciently low impedance at high frequencies toproduce on said first resistance a voltage which combines with thevoltage supplied to said input through said second resistance to producebetween said grid and cathode a resultant voltage having a degenerativephase at high frequencies.

JOSEPH A. WORCESTER, JR.

